6. I have the materials for a monograph upon the Acalephae and Hydrostatic Acalephae. I have examined very carefully more than forty genera of these animals--many of them very rare, and some quite new. But I paid comparatively little attention to the collection of new species, caring rather to come to some clear and definite idea as to the structure of those which had indeed been long known, but very little understood. Unfortunately for science, but fortunately for me, this method appears to have been somewhat novel with observers of these animals, and consequently everywhere new and remarkable facts were to be had for the picking up.